Replace elementHasLegalLinkAttribute() helper with virtual function

Source/core/html/HTMLBodyElement.cpp

Index: Source/core/html/HTMLBodyElement.cpp
diff --git a/Source/core/html/HTMLBodyElement.cpp b/Source/core/html/HTMLBodyElement.cpp
index 10882eac5d59c043e360ac1d768b6a558226c640..1bbb6178e381fdf20e72c1f28fec5016ec476f31 100644
--- a/Source/core/html/HTMLBodyElement.cpp
+++ b/Source/core/html/HTMLBodyElement.cpp
@@ -179,6 +179,11 @@ bool HTMLBodyElement::isURLAttribute(const Attribute& attribute) const
     return attribute.name() == backgroundAttr || HTMLElement::isURLAttribute(attribute);
 }
 
+bool HTMLBodyElement::hasLegalLinkAttribute(const QualifiedName& name) const
+{
+    return name == backgroundAttr || HTMLElement::hasLegalLinkAttribute(name);
+}
+
 bool HTMLBodyElement::supportsFocus() const
 {
     // This override is needed because the inherited method bails if the parent is editable.